This invention relates to frequency generators and, more particularly, to improved method and apparatus for generating a plurality of carrier frequencies symmetrically disposed about a high-frequency signal.
In many multiplex communication systems, a number of closely spaced carrier frequencies are required to provide the basic separation between carrier channels. For example, in frequency division multiplex systems which employ single sideband modulation techniques, carrier frequencies often are spaced at 4 kHz intervals. Further, in order to take advantage of the light weight and small size of present day polylithic crystal filters, such carrier frequencies are required to be in the 8 mHz range. Of course, the carriers could be obtained by providing a separate oscillator for each desired frequency. However, this is not only expensive but introduces a problem of stabilizing a plurality of units rather than reducing this stability problem to a single unit or perhaps one or two units. Another technique is to use a high-frequency as a carrier and to use a modulating frequency which is equal to the channel spacing to modulate the high-frequency and provide harmonically related signals at its output. A disadvantage of this technique is the number of components required to obtain the desired result.